The present invention relates to an elevator for lifting and lowering thin sheet-like articles, such as glass substrates and semiconductor substrates (hereinafter referred to as wafers), one by one.
When various wafers are surface-treated, for example, when a resist is to be applied to the surface, there are cases where wafer transfer level differs from place to place such that between the coater and a device for printing a predetermined pattern on the resist-coated wafer, the transfer passage for the treating process using a chemical liquid is at a high position, while that for the exposure process not using any chemical liquid is a low position. Further, the transfer level sometimes also differs between the exposure device and the developing device subsequent thereto.
Conventionally, in the resist applying process, from a cassette containing a predetermined number of wafers, the wafers are delivered one by one, coated with a resist by a rotary coater, and dried in an oven, whereupon they are stored one by one in another cassette. The cassette thus storing a predetermined number of wafers is then transferred to the loader of the exposure device in the subsequent process by hand or by a transfer robot.
Thus, according to the conventional method of transferring wafers, cassettes each containing a predetermined number of wafers are transferred through various processes different in level. This method, however, has disadvantages that the long waiting period required results in impurites adhering to wafers and that there is danger of damaging wafers during transfer.
It is an object of the present invention to provide an appratus for automatically transferring wafer one by one by an elevator between transfer passages locating at different levels, for example, between a coater and an exposure device.